我在mainActivity中有asynctask并将数据保存到sqlite.But当我在viewpager frags中加载这些数据时，它在一个工作正常，而第二个片段没有发生任何事情。有人可以帮助我吗？
public class CurrentContests extends Fragment {
private String TAG = CurrentContests.class.getSimpleName();
RecyclerView rv;
ProgressDialog pdialog;
public DataAdapter adapter;
protected static ArrayList<DataModel> data;
private RecyclerView.LayoutManager layoutManager;
static View v;
private static final String SELECT_SQL = "SELECT * FROM ankit";
public SQLiteDatabase db;
private Cursor c;
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
v = inflater.inflate(R.layout.currentcontests_layout, container, false);
data = new ArrayList<>();
rv = (RecyclerView) v.findViewById(R.id.tab1_recycler_view);
rv.setHasFixedSize(true);
layoutManager = new LinearLayoutManager(getActivity());
rv.setLayoutManager(layoutManager);
rv.setItemAnimator(new DefaultItemAnimator());
adapter = new DataAdapter(data);
rv.setAdapter(adapter);
/* new GetContacts().execute();*/
openDatabase();
c = db.rawQuery(SELECT_SQL, null);
//c.moveToFirst();
//showRecords();
db.beginTransaction();
shownow();
return v;
}
protected void openDatabase() {
db =getActivity().openOrCreateDatabase("ankitDB", Context.MODE_PRIVATE, null);//openOrCreateDatabase("ankitDB", Context.MODE_PRIVATE, null);
}
private void shownow(){
//if the cursor isnt null we will essentially iterate over rows and then columns
//to form a table of data as per database.
if (c != null) {
//more to the first row
c.moveToFirst();
Log.e("current", "shownow");
//iterate over rows
for (int i = 0; i < c.getCount(); i++) {
String site = c.getString(1);
String name = c.getString(2);
String begin_date = c.getString(3);
String begin_time=c.getString(4);
String end_date=c.getString(5);
String end_time=c.getString(6);
String type=c.getString(7);
//String type=c.getString(8);
DataModel dm = new DataModel(site, name, begin_date, begin_time, end_date, end_time);//,i+1,R.drawable.codechef);
data.add(dm);
//move to the next row
c.moveToNext();
}
//close the cursor
db.setTransactionSuccessful();
db.endTransaction();
c.close();
db.close();
}
adapter.notifyDataSetChanged();
}
}
这是我的 Second Fragment
public class SecondContent extends Fragment {
private String TAG = UpcommingContests.class.getSimpleName();
RecyclerView rv;
ProgressDialog pdialog;
public DataAdapter adapter;
protected static ArrayList<DataModel> data;
private RecyclerView.LayoutManager layoutManager;
static View v;
private static final String SELECT_SQL = "SELECT * FROM ankit";
public SQLiteDatabase dbup;
private Cursor cup;
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
v = inflater.inflate(R.layout.upcomingcontests_layout, container, false);
data = new ArrayList<>();
rv = (RecyclerView) v.findViewById(R.id.rv_tab2);
rv.setHasFixedSize(true);
layoutManager = new LinearLayoutManager(getActivity());
rv.setLayoutManager(layoutManager);
rv.setItemAnimator(new DefaultItemAnimator());
adapter = new DataAdapter(data);
rv.setAdapter(adapter);
/* new GetContacts().execute();*/
openDatabase();
cup = dbup.rawQuery(SELECT_SQL, null);
//c.moveToFirst();
//showRecords();
shownow();
return v;
}
protected void openDatabase() {
dbup =getActivity().openOrCreateDatabase("ankitDB", Context.MODE_PRIVATE, null);//openOrCreateDatabase("ankitDB", Context.MODE_PRIVATE, null);
}
private void shownow(){
//if the cursor isnt null we will essentially iterate over rows and then columns
//to form a table of data as per database.
if (cup != null) {
//more to the first row
cup.moveToFirst();
Log.e("upcoming","shownow");
//iterate over rows
for (int i = 0; i < cup.getCount(); i++) {
String site = cup.getString(1);
String name = cup.getString(2);
String begin_date = cup.getString(3);
String begin_time=cup.getString(4);
String end_date=cup.getString(5);
String end_time=cup.getString(6);
String type=cup.getString(7);
//String type=c.getString(8);
Log.e("upcoming",site+"");
DataModel dm = new DataModel(site, name, begin_date, begin_time, end_date, end_time);//,i+1,R.drawable.codechef);
data.add(dm);
//move to the next row
cup.moveToNext();
}
//close the cursor
adapter.notifyDataSetChanged();
cup.close();
dbup.close();
}
adapter.notifyDataSetChanged();
}
}
答案 0 :(得分：0)
问题可能出在数据库事务管理中。当事务启动时，它会阻止从任何其他位置访问数据库，直到它结束。
在您的情况下，您在onCreateView()中启动事务并仅在游标不为空时才完成。这意味着如果光标为空，数据库将保持阻塞状态。
首选使用try-finally块中的数据库事务来防止此类行为：
db.beginTransaction();
try {
// do your work
db.setTransactionSuccessful();
} catch {
//Error between database transaction. Or skip catch if not necessary
} finally {
db.endTransaction();
}